Basic example

#ros2   #parameter   #param   #python  

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Table of Content

ROS2 Params basic example

Simple node with params, run the node from cli and launch file, control the parameters from cli or yaml file

node

import rclpy
from rclpy.node import Node

class BasicParams(Node):
    def __init__(self):
        super().__init__('basic_param')
        self.get_logger().info("start basic param")
        self.declare_parameter('my_str', value="string data")
        self.declare_parameter('my_int', value=10)

        self.my_str = self.get_parameter("my_str").value
        self.my_int = self.get_parameter("my_int").value

        self.get_logger().info(f"my_str: {self.my_str}")
        self.get_logger().info(f"my_int: {self.my_int}")


def main(args=None):
    rclpy.init(args=args)
    node = BasicParams()
    rclpy.spin(node)
    node.destroy_node()
    rclpy.shutdown()

if __name__ == "__main__":
    main()

usage

cli

use default

simple run

ros2 run pkg_python_tutorial param_basic 
[INFO] [1674810902.438001696] [basic_param]: start basic param
[INFO] [1674810902.438464027] [basic_param]: my_str: string data
[INFO] [1674810902.438649552] [basic_param]: my_int: 10

init from cli

init from params from cli

ros2 run pkg_python_tutorial param_basic --ros-args -p my_int:=20 -p my_str:="hello world"
[INFO] [1674811321.921565297] [basic_param]: start basic param
[INFO] [1674811321.921986535] [basic_param]: my_str: hello world
[INFO] [1674811321.922149889] [basic_param]: my_int: 20

load from yaml file

param file structure

<node name>:
    ros__parameters:
        <param_name>: <param_value>

basic.yaml

basic_param:
  ros__parameters:
    my_int: 100
    my_str: hello yaml

Tip

Add copy instruction to data_files section

data_files=[
    (os.path.join('share', package_name, "config"), glob('config/*.yaml'))
]

init from yaml file

ros2 run pkg_python_tutorial param_basic --ros-args  --params-file  config/basic.yaml

mix yaml and param

# the last setting 
ros2 run pkg_python_tutorial param_basic --ros-args  --params-file  config/basic.yaml -p my_int:=10

# if the param cli set the value after the param yaml file , the value from the parameter is set
# if the param is set before the yaml file, the value from the yaml file is set

---

launch

set param in launch file

node_with_param.launch.py

from launch import LaunchDescription
from launch_ros.actions import Node

def generate_launch_description():
    ld = LaunchDescription()

    sim_node =  Node(
            package='pkg_python_tutorial',
            namespace='',
            executable='param_basic',
            name='basic',
            parameters=[
                {
                    "my_str": "data from launch",
                    "my_int": 100
                }
            ]
        )
    ld.add_action(sim_node)
    return ld

load param from yaml in launch file

node_with_param_file.launch.py

import os
from launch import LaunchDescription
from ament_index_python.packages import get_package_share_directory
from launch_ros.actions import Node

def generate_launch_description():
    ld = LaunchDescription()

    config = os.path.join(
        get_package_share_directory('pkg_python_tutorial'),
        'config',
        'params.yaml'
        )

    sim_node =  Node(
            package='pkg_python_tutorial',
            namespace='',
            executable='param_basic',
            name='basic',
            parameters=[config]
        )
    ld.add_action(sim_node)
    return ld

params.yaml

basic:
  ros__parameters:
    my_str: "launch and load from yaml"
    my_int: 100

node /yaml name

The node name in yaml file need to be the same name we set in the launch file Node.name property

load param from yaml with override by local launch params

```python title=”” linenums=”1” hl_lines=”6,8,9” sim_node = Node( package=’simples’, namespace=’‘, executable=’param_basic’, name=’basic_param’, parameters=[config, { “my_str”: “override”, “my_int”: 1 }
] )

---

### rqt

```bash
ros2 run rqt_reconfigure rqt_reconfigure
# or
# run rqt_gui and load th dynamic_reconfiguration plugin